Refrigeration system with auxiliary defrost heat tank

ABSTRACT

A refrigeration system adapted to cycle alternately through a refrigeration cycle and a defrost cycle, wherein a suction accumulator tank is provided in the suction line between the evaporator and the compressor to receive any liquid refrigerant discharged from the evaporator toward the compressor during the hot gas defrost cycle. An auxiliary defrost heat tank is connected to the suction accumulator tank having a coil immersed in a heated heat storage liquid to receive liquid refrigerant from the suction accumulator when the liquid level in the latter exceeds a predetermined reference level and evaporates the liquid refrigerant for return in gaseous state to the suction accumulator.

United States Patent Morris, Jr. 1 1 Dec. 2, 1975 [5 1 REFRIGERATION SYSTEM WITH 3,071,935 1/1963 Kapeker 62/278 AUXILIARY DEFROST HEAT TANK 3,792,594 2/1974 Kramer 62/278 [76] Inventor: William Morris, Jr., 801 Primary Examiner william J. Wye

Fayettevlne Ralelgh Attorney, Agent, or FirmMason, Fenwick & 27601 Lawrence [22] Filed: Sept. 12, 1974 [21] Appl. No.: 505,347 [57] ABSTRACT A refrigeration system adapted to cycle alternately through a refrigeration cycle and a defrost cycle, {52] U.S. Cl. 62/156; 62/275; 62/352 wherein a Suction accumulator tank is Provided in the [5 l] Int. Cl. F25D 21/06 suction line between the evaporator and the compres [58] Field of Search 62/278, 81, 8O, sor to receive any liquid refrigerant discharged from 62/351 156 the evaporator toward the compressor during the hot gas defrost cycle. An auxiliary-defrost heat tank is [56] References Cited connected to the suction accumulator tank having a UNITED STATES PATENTS coil immersed in a heated heat storage liquid to re- 2,440,146 4/1948 Kramer 62/278 Ceive liquid refrigerant from the Suction accumulator 2,641,908 6/1953 La Porte 62/278 when the liquid level in the latter exceeds a predeter- 2,770,104 11/1956 Sweynor 62/278 mined reference level and evaporates the liquid refrig- 3 8H957 Haflsenm" 62/278 erant for return in gaseous state to the suction accu- 2,819,592 1/1958 Smith 62/276 l 3,012,414 12/1961 La Porte 62/278 3,012,415 12/1961 La Porte 62/278 20 C 2 Drawing Figures SUCTION Acwmumm GVAPOIZRTQ Z,

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US. Patent Dec. 2, 1975 SUCTION Amumumwrora.

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CONDENSOIZ EECEWEB REFRIGERATION SYSTEM WITH AUXILIARY DEFROST HEAT TANK BACKGROUND AND OBJECTS OF THE INVENTION The present invention relates in general to reversible cycle refrigeration systems, and more particularly to refrigeration systems for ice-making or cooling purposes which are cycled alternately through a freezing phase and a harvesting or defrosting phase, and which employ a suction accumulator or knock-out tank in the return line from the evaporator to the compressor.

While the present invention is applicable to liquid chilling applications, cooled storage room refrigeration, and like applications as well as automatic icemaking apparatus, it will be described specifically in connection with a reversible cycle refrigeration system for automatic production of ice employing hot gaseous refrigerant for defrosting or harvesting of the ice.

Automatic ice-making reversible cycle refrigeration systems have gone into wide commercial use. In suchsystems, ice is produced, frequently in the form of an elongated tube or annular cylinder, during the normal refrigeration or freezing phase of the apparatus when condensed liquid refrigerant is admitted to the evaporator from the receiver or condenser-receiver, and the ice is discharged from the evaporator during the defrosting or harvesting phase when hot gaseous refrigerant is delivered directly from the compressor to the evaporator in bypassing relation to the condenser. Such systems have customarily involved an evaporator having a refrigerant chamber which contains a large volume of liquid refrigerant at the conclusion of the freezing cycle. To accomplish proper defrosting and release of the ice from the evaporator by hot gaseous refrigerant and avoid an undesirable amount of melting of the ice as the hot gaseous refrigerant releases the frost bond between the ice and the evaporator ice-forming surfaces, it is desirable to pump down the liquid which occupies the evaporator at the end of the freezing cycle as rapidly as possible, and typically a device known as a suction accumulator or knock-out tank is provided in the suction line between the evaporator and the compressor to receive any liquid refrigerant which passes into the suction conduit from the evaporator to attempt to reevaporate or boil off the liquid carried over from the evaporator and thereby avoid transfer to the compressor of liquid refrigerant at the commencement of and during the defrost cycle which might damage the compressor.

In the typical installation, the suction accumulator of standard design during the normal refrigeration cycle of a reverse cycle single compressor hot gas defrost system utilizes a heat transfer liquid boil-out coil within the accumulator through which warm liquid refrigerant from the receiver flows to the evaporator, with this liquid boil-out coil in heat exchange relation with the liquid refrigerant carried over from the evaporator through the suction conduit connected to the evaporator outlet to boil ofl most of the liquid refrigerant, sometimes termed liquid slop-over that is carried over from the evaporator. Typically the suction conduit from the suction accumulator to the suction side of the compressor is connected to a U-shaped tube within the suction accumulator which has an open end near the top of the interior of the suction accumulator above the normal liquid level therein, and a metering orifice is 2 frequently provided in the bottom of the U-bend in this U-shaped suction line in the suction accumulator to carry back to the compressor at a controlled rate by aspiration through the metering orifice a small amount of the oil-rich refrigerant liquid in the accumulator.

It has been found that such suction accumulators of standard design, when employed in reverse cycle single compressor hot gas defrost systems are inadequate to properly protect the compressor against return of slugs of liquid refrigerant to the compressor, during the defrost cycle and at the commencement of the defrost cycle. Clearly the liquid boil-out coil in the suction accumulator of standard design is ineffective during the defrost cycle, because there is no flow of liquid refrigerant from the receiver to the evaporator during the defrost cycle of the system. At the same time, it must be realized that it is when the system is in defrost phase that there is the greatest volume of liquid refrigerant return or slop-over into the suction accumulator, resulting from the blast of hot gas into the evaporator as the hot gas solenoid opens, bringing all the liquid in the evaporator over at once, and during the defrost cycle there is added to this the additional liquid that results from the defrosting action of the hot gas in the evaporator in contact with the cold evaporator surface. This condition results in a maximum amount of slop-over or return liquid refrigerant building up in the suction accumulator during this defrost period of the cycle, with the metering orifice at the bottom of the U-tube in the accumulator being the only means of removing the refrigerant which is then liquid state in the accumulator.

In the typical type of single compressor reverse cycle hot gas defrost system, the only sources of heat are (a) the flash gas from the condenser which occurs within approximately ten to fifteen seconds after the hot gas solenoid valve which delivers hot gaseous refrigerant to the evaporator opens, (b) any residual heat from the mass of the compressor unit itself, that may be picked up by wet refrigerant suction gas and carried over to the cold evaporator surface as the compressor functions as a circulation pump during defrost cycle, and (c) the heat equivalent of the motor energy of the compressor motor which rep resents the work being done by the compressor on the refrigerant as it is circulated. In reverse cycle refrigeration systems in which an effective defrost, for example to harvest ice, can be accomplished rather quickly, for example in 3 to 5 minutes, these sources of heat are frequently effective and are the simplest means of accomplishing a hot gas defrost. If, however, an extended defrost is required for any reason, such as may occur with certain structural designs of evaporators, this type system becomes rather ineffective after the first 3 minutes of defrost because all available heat from both the condenser flash gas and the residual heat from the mass of the compressor are depleted by that time and the only remaining heat available is from the heat equivalent of the work being done by the compressor on the refrigerant as it is circulated, which is quite limited.

An object of the present invention is the provision of a refrigeration system of the reversible cycle single compressor hot gas defrost type having a suction ,accumulator in the suction line between the evaporator and the compressor, wherein means are associated with the suction accumulator to increase the heat available for defrost and shorten the defrost cycle with a minimum of complications and expense and without loss of efficiency or capacity during the refrigeration cycle.

Another object of the present invention is the provision of a refrigration system of the reverse cycle single compressor hot gas defrost type having a suction accumulator, wherein an auxiliary defrost heat tank is coupled with the suction accumulator to receive during the defrost cycle some of the return liquid refrigerant carried over from the evaporator to the suction accumulator to rapidly evaporate the return liquid refrigerant received from the suction accumulator and contribute to the effectiveness of the defrost cycle. The auxiliary defrost heat tank receives no liquid refrigerant from the suction accumulator during the refrigeration cycle, and therefore does not introduce any loss of efficiency or capacity during the refrigeration cycle.

Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing illustrating a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a diagrammatic view of a reverse cycle single compressor refrigeration system with automatic hot gas defrost, embodying the present invention; and

FIG. 2 is an enlarged vertical section view of the suction accumulator and auxiliary defrost heat tank and conduit interconnections therebetween, showing the interior construction of these components.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings, wherein like reference characters designate corresponding parts throughout the several figures, the automatic ice-making refrigeration system of the reverse cycle single compressor hot gas defrost system type illustrated as a preferred example in FIG. 1 includes the usual motor driven compressor having the usual high pressure discharge port connected directly to the high pressure compressor discharge line 1 1 and a low pressure suction port to which a suction line segment herein referred to as the compressor suction line 12 is connected. The high pressure discharge line divides into two branch lines, one being indicated by the reference character 13 which leads to the condenser, or condenser-receiver and forms the condenser inlet or refrigerant supply line 13, and the other branch, indicated by the reference character 15, forming the hot gas bypass line for admitting the hot gaseous refrigerant from the high pressure compressor discharge line 11 directly to the inlet of the evaporator 16. The condenser-receiver 14 in the preferred embodiment is of the usual water-cooled type and has an outlet port connected by liquid line 17 to the bottom inlet of the conventional spiral coil forming the liquid boil-out coil, indicated at 18 in FIG. 2, of the suction accumulator or knock-out tank 19. The uppper outlet of the spiral coil 18 in the suction accumulator is connected through liquid refrigerant supply line 20, which in the preferred embodiment has a liquid solenoid valve 21 therein, to the thermostatic expansion valve 22 and into the inlet 23 of the evaporator 16. The evaporator 16 may be of any conventional or known evaporator construction, which for example may be of the single annular cylindrical evaporator configuration such as that shown in earlier C. E. Lowe US. Pat. No. 3,146,610 or it may comprise a plurality of evaporator sections of known configuration, or in one preferred embodiment may be in the form of a plurality of evaporator sections in an automatic cube ice-making machine such as that disclosed in my earlier US. Pat. No. 3,766,744. If the refrigeration system of the present invention is employed with a plurality of evaporator sections for making ice, the liquid refrigerant supply line 20 may connect through the liquid solenoid valve 21 and thermostatic expansion valve 22 to a liquid distributor of known construction for distributing liquid in proper order and proportion to the various evaporator sections rather than supplying the liquid refrigerant to a single inlet as when a single evaporator chamber is to be supplied with refrigerant.

The vapor phase refrigerant is returned from the evaporator 16 or plurality of evaporator sections through an evaporator suction outlet line 24, which in the case of. plural evaporator sections may connect to an elongated suction header or manifold connected to each of the evaporator sections, which returns the vapor phase refrigerant to a gas inlet opening in the upper region of the cylindrical sidewall of the suction accumulator or knock-out tank 19. In addition to the spiral coil 18 which conveys warm liquid refrigerant during the refrigeration cycle from the receiver or the condenser-receiver to the thermostatic expansion valve and evaporator inlet, the suction accumulator 19 also includes the usual U-tube, indicated at 25 in FIG. 2, having an open end near the top of the accumulator tank into which the returning refrigerant gas which evaporates in the suction accumulator is drawn and conveyed by the compressor suction line 12 which connects to the U-tube 25 where it exits from the top of the suction accumulator tank 19.

An auxiliary defrost heat tank, indicated by the reference character 26 is coupled with the suction accumulator 19 in the system of the present invention, and comprises what may be described as a heat storage tank containing a suitable liquid, such as a glycol solution, which is heated from the suitable source, for example, by electric heat or heat from the compressor discharge line passing through the liquid in the tank 26, to store heat and provide heated liquid which can be placed in thermal exchange relation with liquid refrigerant from the suction accumulator 19 when the latter reaches a predetermined level during defrost cycle to assist in evaporating the return liquid refrigerant and shorten the defrost cycle. The auxiliary defrost heat tank 26 includes a generally cylindrical tank receptacle 27 having a fill inlet 28 closed by removable cap and a relief valve 29 at the top, in the preferred embodiment, and having a spiral coil 30 of conduit tubing located within the tank receptacle 27, for example over about the upper half of the receptacle 27, with the outlet end of the coil 30 connected to a return line 31 to the accumulator opening, for example, into the suction return line 24 from the evaporator just before it enters the inlet port to the suction accumulator 19. The inlet end of the spiral coil 30 connects by a feed line 32 to the suction accumulator 19 at a location slightly above the normal liquid level, indicated by the reference character 33, in the suction accumulator 19 of the liquid refrigerant occupying the suction accumulator during the normal refrigeration cycle. The location of the inlet to the feed line 32 is, however, sufficiently low so that a large portion of the additional return liquid or slop-over liquid from the evaporator occupying the level above the normal liquid refrigerant level 33 for normal refrigeration cycle operation will be gravity conveyed through the feed line 32 and the spiral coil 30 into thermal exchange relation with the body of liquid, indicated at 34, in the auxiliary defrost heatt tank 26. In a preferred embodiment, the auxiliary defrost heat tank 26 is supplied with heat by an electric heating element 35, connected for example by wiring with a conventional thennostatic control, to heat the heat storage liquid, for example the glycol solution, in the tank 26 to a temperature of approximately 150-l 80F. Alternately, instead of employing an electric heat source, the compressor discharge line 11 from the compressor may pass through or in thermal exchange relation with the heat storage liquid 34 in the tank 26 to heat the liquid to the l50l80F. range.

In the normal refrigeration cycle of the system, the hot gaseous refrigerant discharge through the compressor discharge line 11 courses into the condenser or condenser-receiver 14 where the refrigerant condenses to liquid phase and accumulates in the receiver or the receiver portion of the condenser-receiver. The condensed liquid refrigerant is supplied from the receiver or receiver section through the liquid line 17 and spiral blow-out coil 18 of the suction accumulator 19, liquid line 20, and open liquid solenoid valve 21 to the expansion valve 22 which meters the liquid refrigerant supplied to the inlet of the evaporator 16 or the distributor distributing the refrigerant to a plurality of evaporator sections. The refrigerant at low pressure in the evaporator or evaporator section extracts heat from the iceforming surface, to freeze water which is, in accordance with conventional practice, flowed downwardly along the ice-forming surfaces of the evaporator or evaporator sections. As the refrigerant extracts heat from these ice-forming surfaces and the water, the refrigerant begins to turn to vapor phase and is withdrawn from the evaporator through the line 24 to the suction accumulator or knock-out tank 19. The returning refrigerant which is in gaseous or vapor phase form enters the open upper end of the U-tube 25 in the accumulator l9 and is withdrawn through the compressor suction line 12 to the suction port of the compressor 10. Any Freon or refrigerant liquid in the lower portion of the suction accumulator 19 is an oil-rich refrigerant liquid and a limited amount of this oil-rich refrigerant liquid is carried back at a control rate through the metering orifice in the bottom of the U-tube in the suction accumulator to return to the compressor. During this normal refrigeration cycle, the lever of liquid refrigerant in the suction accumulator 19 slopped-over or returned from the evaporator is normally below the level at which the feed line 32 to the auxiliary defrost heat tank 26 connects into the sidewall of the tank receptacle 19, so that no liquid will spill over from the accumulator tank 19 into the auxiliary defrost heat tank 26 during this normal refrigeration cycle and the temperature of the heat-storing liquid 34 in the tank 26 is built up to the range of l50l80F. while the system is in this normal refrigeration cycle state.

When the appropriate thickness of ice has developed on the evaporator surfaces or for any other reason shift to the hot gas defrost mode or cycle is desired, the solenoid valve 21 in the liquid supply line 20 is closed and the hot gas solenoid 36 in the hot gas bypass line is opened. The hot gaseous refrigerant from the high pressure discharge line 11 of the compressor 10 then passes through the hot gas line 15 to the evaporator to supply heat to. the evaporator surfaces for defrosting the frost bond'holding the ice on the evaporator surfaces and effect gravity discharge of the-ice into a suitable collecting bin or trough as the frost bond is destroyed. Flash gas from the condenser, if the system is of the type disclosed in my earlier US. Pat. No. 3,766,744, will also contribute heat to the defrosting of the frost bond, and in fact serves as the primary source of heat for defrosting during the initial phases of the harvesting cycle. The blast of hot gas which is delivered through the defrost line 15 to the evaporator as the hot gas solenoid 36 opens brings substantially all of the liquid in the evaporator or evaporator sections over at once into the suction accumulator 19 through the evaporator return line 24 and any additional liquid phase refrigerant that condenses as a result of the defrosting action of the hot gas in contact with the cold evaporator surface also adds to the accumulation of liquid refrigerant in the suction accumulator. The metering orifice at the bottom of the U-tube in the accumulator 19 being inadequate to remove the return or slop-over liquid refrigerant, the liquid level in the suction accumulator promptly builds up above the level of the inlet to the feed line 32, and the cold liquid refrigerant thus returned spills over into the spiral coil 30 in the auxiliary heat tank 26 in thermal exchange relation with the 1-50l80F. liquid 34 in the tank 26. This achieves almost instant evaporation of the slop-over or return liquid refrigerant conveyed through the feed line 32 into the spiral coil 30 because of the high temperature heat storage liquid 34 in the heat tank 26, and the vapor phase refrigerant in the coil 30 then returns to the upper portion of the suction accumulator 19 through the return line 31 where it is drawn into the open upper end of the U-tube 25 and returns through compressor suction line 12 to the compressor inlet port. The heat tank 26 thus provides a substantial heat load almost instantaneously and contributes substantially to the cf fectiveness of the defrost cycle as well as increasing the capacity of the refrigeration system by shortening the time required to complete the defrost cycle. Since this increase in liquid level of the return liquid in the suction accumulator 19 raising it high enough to spill liquid refrigerent over into the defrost heat tank 26 through the feed line 32 occurs only during the defrost cycle, there is no adverse effect upon the capacity or efficiency of the system during the normal refrigeration cycle. Also, this arrangement is positive simple, relatively inexpensive and maintenance free since it requires no valves or controls and is dependent only upon gravity to effect transfer of liquid refrigerant through the feed line 32 to the defrost heat tank when the liquid level rises sufficiently in the suction accumulator during the defrost cycle. The auxiliary heat tank also provides extra capacity against liquid slop-over in addition to that provided by the suction accumulator in the event of malfunction of an expansion valve or other liquid control devices.

I claim:

1. A refrigeration system adapted to cycle alternately through a refrigeration cycle and a defrost cycle, comprising a compressor having discharge and suction ports, a condenser connected to the discharge port to receive refrigerant gas from the compressor during the refrigerant cycle and condense the same, an evaporator having an inlet connected to the condenser to receive condensed liquid refrigerant therefrom during the refrigeration cycle and having an outlet, hot gas conduit means for conveying gaseous refrigerant from the compressor to the evaporator during the defrost cycle, a suction accumulator tank connected by an outlet suction line to the suction port of the compressor and by an inlet suction line to the evaporator outlet for receiving any liquid refrigerant discharged from the evaporator outlet toward the compressor and having means for conveying warm liquid refrigerant coursing from the condenser to the evaporator therethrough in heat exchange relation with liquid refrigerant in the accumulator tank received from the evaporator outlet to vaporize the latter, an auxiliary defrost heat tank connected to said suction accumulator tank substantially filled with a heat storage liquid and having a conduit coil immersed therein connected by a feed line to said accumulator tank at a location slightly above a reference liquid level therein normally reached by the liquid refrigerant during the refrigeration cycle to convey liquid refrigerant during the defrost cycle to the heat tank only when the liquid refrigerant level in the accumulator tank exceeds said reference level, means for heating said heat storage liquid in said heat tank to a sufficient temperature for promptly vaporizing any liquid refrigerant conveyed into said conduit coil therein, and a heat tank outlet conduit for return of the vaporized refrigerant from the conduit coil in the heat tank to the suction port of said compressor.

2. A refrigeration system as defined in claim 1, wherein said heat tank includes an electric heating element immersed in the heat storage liquid therein to heat the same to a predetermined temperature for vaporizing the liquid refrigerant conveyed into said conduit coil.

3. A refrigeration system as defined in claim 2, including thermostatic control means for controlling electric supply to said heating element to attain temperature in said heat storage liquid in the range of about 150F to 180F.

4. A refrigeration system as defined in claim 1, wherein said means for heating said heat storage liquid in said heat tank comprises conduit means extending therethrough .for conveying hot gaseous refrigerant from said discharge port of said compressor before delivery of the hot gaseous refrigerant to said condenser or said evaporator to heat the heat storage liquid to a temperature range of about 150F to 180F.

5. A refrigeration system as defined in claim 1, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.

6. A refrigeration system as defined in claim 3, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.

7. A refrigeration system as defined in claim 4, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.

8. A refrigeration system as defined in claim 1,. wherein said heat tank outlet conduit comprises a return line from a return end of said'conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tankto return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.

9. A refrigeration system as defined in claim 3, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.

10. A refrigeration system as defined in claim 4, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.

11. A refrigeration system adapted to cycle alternately through a refrigeration cycle and a defrost cycle, comprising a compressor having discharge and suction ports, a condenser connected to the discharge port to receive refrigerant gas from the compressor during the refrigerant cycle and condense the same, an evaporator having an inlet connected to the condenser to receive condensed liquid refrigerant therefrom during the refrigeration cycle and having an outlet, hot gas conduit means for conveying gaseous refrigerant from the compressor to the evaporator during the defrost cycle, a suction accumulator tank connected by an outlet suction line to the suction port of the compressor and by an inlet suction line to the evaporator outlet for receiving any liquid refrigerant discharged from the evaporator outlet toward the compressor, an auxiliary defrost heat tank connected to said suction accumulator tank substantially filled with a heat storage liquid and having a conduit coil immersed therein connected by a feed line to said accumulator tank at a location slightly above a reference liquid level therein normally reached by the liquid refrigerant during the refrigeration cycle to convey liquid refrigerant during the defrost cycle to the heat tank only when the liquid refrigerant level in the accumulator tank exceeds said reference level, means for heating said heat storage liquid in said heat tank to a sufficient temperature for promptly vaporizing any liquid refrigerant conveyed into said conduit coil therein, and a heat tank outlet conduit for return of the vaporized refrigerant from the conduit coil in the heat tank to the suction port of said compressor.

12. A refrigeration system as defined in claim 11, wherein said heat tank includes an electric heating element immersed in the heat storage liquid therein to heat the same to a predetermined temperature for vaporizing the liquid refrigerant conveyed into said conduit coil.

13. A refrigeration system as defined in claim 12, in-

eluding thermostatic control means for controlling electric supply to said heating element to attain temperature in said heat storage liquid in the range of about F to F.

14. A refrigeration system. as defined in claim 11, wherein said means for heating said heat storage liquid 9 in said heat tank comprises conduit means extending therethrough for conveying hot gaseous refrigerant from said discharge port of said compressor before delivery of the hot gaseous refrigerant to said condenser or said evaporator to heat the heat storage liquid to a temperature range of about 150F to 180F.

15. A refrigeration system as defined in claim 11, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.

16. A refrigeration system as defined in claim 13, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.

17. A refrigeration system as defined in claim 14,

wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refriger- 10 ant level in the accumulator tank exceeds said reference liquid level.

18. A refrigeration system as defined in claim 11, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.

19. A refrigeration system as defined in claim 13, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.

20. A refrigeration system as defined in claim 14, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor. 

1. A refrigeration system adapted to cycle alternately through a refrigeration cycle and a defrost cycle, comprising a compressor having discharge and suction ports, a condenser connected to the discharge port to receive refrigerant gas from the compressor during the refrigerant cycle and condense the same, an evaporator having an inlet connected to the condenser to receive condensed liquid refrigerant therefrom during the refrigeration cycle and having an outlet, hot gas conduit means for conveying gaseous refrigerant from the compressor to the evaporator during the defrost cycle, a suction accumulator tank connected by an outlet suction line to the suction port of the compressor and by an inlet suction line to the evaporator outlet for receiving any liquid refrigerant discharged from the evaporator outlet toward the compressor and having means for conveying warm liquid refrigerant coursing from the condenser to the evaporator therethrough in heat exchange relation with liquid refrigerant in the accumulator tank received from the evaporator outlet to vaporize the latter, an auxiliary defrost heat tank connected to said suction accumulator tank substantially filled with a heat storage liquid and having a conduit coil immersed therein connected by a feed line to said accumulator tank at a location slightly above a reference liquid level therein normally reached by the liquid refrigerant during the refrigeration cycle to convey liquid refrigerant during the defrost cycle to the heat tank only when the liquid refrigerant level in the accumulator tank exceeds said reference level, means for heating said heat storage liquid in said heat tank to a sufficient temperature for promptly vaporizing any liquid refrigerant conveyed into said conduit coil thereIn, and a heat tank outlet conduit for return of the vaporized refrigerant from the conduit coil in the heat tank to the suction port of said compressor.
 2. A refrigeration system as defined in claim 1, wherein said heat tank includes an electric heating element immersed in the heat storage liquid therein to heat the same to a predetermined temperature for vaporizing the liquid refrigerant conveyed into said conduit coil.
 3. A refrigeration system as defined in claim 2, including thermostatic control means for controlling electric supply to said heating element to attain temperature in said heat storage liquid in the range of about 150*F to 180*F.
 4. A refrigeration system as defined in claim 1, wherein said means for heating said heat storage liquid in said heat tank comprises conduit means extending therethrough for conveying hot gaseous refrigerant from said discharge port of said compressor before delivery of the hot gaseous refrigerant to said condenser or said evaporator to heat the heat storage liquid to a temperature range of about 150*F to 180*F.
 5. A refrigeration system as defined in claim 1, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.
 6. A refrigeration system as defined in claim 3, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.
 7. A refrigeration system as defined in claim 4, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.
 8. A refrigeration system as defined in claim 1, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.
 9. A refrigeration system as defined in claim 3, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.
 10. A refrigeration system as defined in claim 4, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.
 11. A refrigeration system adapted to cycle alternately through a refrigeration cycle and a defrost cycle, comprising a compressor having discharge and suction ports, a condenser connected to the discharge port to receive refrigerant gas from the compressor during the refrigerant cycle and condense the same, an evaporator having an inlet connected to the condenser to receive condensed liquid refrigerant therefrom during the refrigeration cycle and having an outlet, hot gas conduit means for conveyiNg gaseous refrigerant from the compressor to the evaporator during the defrost cycle, a suction accumulator tank connected by an outlet suction line to the suction port of the compressor and by an inlet suction line to the evaporator outlet for receiving any liquid refrigerant discharged from the evaporator outlet toward the compressor, an auxiliary defrost heat tank connected to said suction accumulator tank substantially filled with a heat storage liquid and having a conduit coil immersed therein connected by a feed line to said accumulator tank at a location slightly above a reference liquid level therein normally reached by the liquid refrigerant during the refrigeration cycle to convey liquid refrigerant during the defrost cycle to the heat tank only when the liquid refrigerant level in the accumulator tank exceeds said reference level, means for heating said heat storage liquid in said heat tank to a sufficient temperature for promptly vaporizing any liquid refrigerant conveyed into said conduit coil therein, and a heat tank outlet conduit for return of the vaporized refrigerant from the conduit coil in the heat tank to the suction port of said compressor.
 12. A refrigeration system as defined in claim 11, wherein said heat tank includes an electric heating element immersed in the heat storage liquid therein to heat the same to a predetermined temperature for vaporizing the liquid refrigerant conveyed into said conduit coil.
 13. A refrigeration system as defined in claim 12, including thermostatic control means for controlling electric supply to said heating element to attain temperature in said heat storage liquid in the range of about 150*F to 180*F.
 14. A refrigeration system as defined in claim 11, wherein said means for heating said heat storage liquid in said heat tank comprises conduit means extending therethrough for conveying hot gaseous refrigerant from said discharge port of said compressor before delivery of the hot gaseous refrigerant to said condenser or said evaporator to heat the heat storage liquid to a temperature range of about 150*F to 180*F.
 15. A refrigeration system as defined in claim 11, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.
 16. A refrigeration system as defined in claim 13, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.
 17. A refrigeration system as defined in claim 14, wherein all of said conduit coil in said heat tank is located below the horizontal level of the feed line connection to said accumulator tank for gravity feed of the liquid refrigerant from the accumulator tank to the conduit coil in said heat tank when the liquid refrigerant level in the accumulator tank exceeds said reference liquid level.
 18. A refrigeration system as defined in claim 11, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.
 19. A refrigeration system as defined in claim 13, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized Refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor.
 20. A refrigeration system as defined in claim 14, wherein said heat tank outlet conduit comprises a return line from a return end of said conduit coil to said inlet suction line immediately upstream from the connection of the latter to said suction accumulator tank to return the vaporized refrigerant from said conduit coil to the upper portion of said suction accumulator tank for return to the compressor. 